There is known a surface acoustic wave sensor for measuring properties or ingredients of an analyte liquid by means of a surface acoustic wave device.
The surface acoustic wave sensor, which is constructed of a piezoelectric substrate on which is mounted a detecting portion which reacts with a component contained in an analyte sample, is designed to detect the properties or ingredients of an analyte liquid by measuring electric signals responsive to variations in surface acoustic wave (SAW) propagating through the detecting portion (for example, refer to Patent Literature 1).
The SAW sensor disclosed in Patent Literature 1 measures the concentration of an analyte sample by detecting a phase difference in SAW. In order to make phase difference measurement, a quadrature modulation system has generally been adopted, because it offers an extended measurable phase range.